1. Field of the Invention
The present invention relates generally to a thyristor which can be controlled by light and having at least four zones of alternating opposite conductivity types.
2. Description of the Prior Art
In the past, thyristors have been designed with at least four zones of alternating opposite conductivity types, in which the first and fourth zones are contacted by the main electrodes and act as emitter zones, the second zone adjoins the first, and the third, least-doped zone is located between the second and fourth zones. Both the second and the third zone, together with the forward-blocking PN-junction formed between them, extend to the surface of the thyristor semiconductor chip on the side with the first zone. The part of the forward-blocking PN-junction which emerges at the surface can be acted on by light for the purpose of triggering the thyristor. There is provided in the said surface a highly doped zone of the conductivity type of the first zone, the latter being connected with the second zone by an electrical contact on the surface.
Such a thyristor is known for instance from DT-OS No. 24 08 079. Although such thyristors have since been utilized with success, further optimization is possible.